1. Field of the Invention
This invention relates to magnetic reed switches and, more particularly, to brackets for mounting a reed switch and an associated magnet on the guide track of an overhead security door.
2. Description of Related Art
A reed switch is a mechanical electrical switch having a pair of ferromagnetic contacts in either a normally-open or normally-closed configuration. In the presence of a magnetic field, the contacts of a normally-open reed switch will close, while the contacts of a normally-closed reed switch will open. Reed switches are typically used as proximity sensors for limit, safety, and security applications.
The present invention is designed for security applications. Overhead security doors are generally mounted between two parallel tracks. For buildings having a height at least double the door height, the tracks may be entirely vertical. However, for buildings having a height less than double the door height, vertical tracks are used for the closed door position, and horizontal tracks are used for the open position. The vertical and horizontal tracks are interconnected by curved sections. As a general rule, overhead doors are secured by a pair of bolts which can be horizontally extended or retracted by rotating a locking handle coupled to both bolts. When the door is fully closed and the bolts are in their extended positions, one bolt is inserted within an aperture in one of the tracks, and the other bolt is inserted within an aperture in the opposite track.
What is needed is a bracket assembly for securely mounting a reed switch and its associated magnet on at least one of the tracks of an overhead door, such that the reed switch and magnet are on opposite sides of the bolt-receiving aperture of the track. If ferromagnetic bolts are employed to lock the door, the bolt will interfere with the magnetic field generated by the magnet so that the reed switch will be unaffected by the magnetic field as long as the bolt is in its locked position. When the bolt is withdrawn from the bolt-receiving aperture, the magnetic field acts on the reed switch to generate a signal. The bracket assembly should, ideally, provide an enclosure which will protect both the reed switch and the magnet from inadvertent mechanical damage. In addition, the bracket assembly should be relatively inexpensive manufacture and simple to install, and readily disassemblable for reed switch replacement.
The present invention fulfills the needs expressed in the background section, in that a bracket assembly for a reed switch and associated magnet is provided that securely mounts to an overhead door track. The assembly is relatively inexpensive to manufacture, simple to install, and readily disassemblable for reed switch or magnet replacement. The assembly also provides an enclosure which protects both the reed switch and the magnet from inadvertent mechanical damage, removal, or misaligning forces. The assembly incorporates an opening that is sized to receive a slidable, locking bolt fabricated from a ferromagnetic material such as mild or hardened steel. The assembly is designed such that the reed switch and magnet mount on opposite sides of the bracket assembly opening. With such an arrangement, the bolt will interfere with the magnetic field generated by the magnet so that the reed switch will be unaffected by the magnetic field as long as the bolt is positioned between the reed switch and the magnet. When the bolt is withdrawn from the bolt-receiving opening of the bracket assembly, the magnetic field acts on the reed switch to generate an electrical signal. Reed switches of both the normally-open and normally-closed varieties may be used in combination with the new bracket assembly. If a normally-open reed switch is used, then the alarm system is set when the switch is open. A closed circuit will trigger a security system alert. Likewise, if a normally-closed reed switch is used, then the alarm system is set when the switch is closed. An open circuit will trigger a security system alert.
The bracket assembly includes first and second interlocking pieces, both of which are stamped from sheet metal which is, preferably, non-ferromagnetic. Each of the pieces incorporates an opening sized to slidably receive a locking door bolt of a given size. For a currently preferred embodiment of the invention, both pieces of the bracket assembly are stamped from sheet aluminum. Both the reed switch and its associated magnet mount may mount on either piece, so long as they are on opposite sides of the opening. For a preferred embodiment of the invention, both the reed switch and the magnet each include a double-stick adhesive layer, one side of which can be exposed by peeling off an attached protective layer. The adhesive layers are employed to attach their associated components to either the first or second piece on either side of the bolt-receiving opening. The first and second pieces reversably snap together to form a box in which the reed switch and the magnet are enclosed. In order to install the bracket assembly on the rail of an overhead door track, screws or rivets are placed through both the first and second pieces and secured to the door track.